Astm d 2285 99

D 2285 – 99 Designation D 2285 – 99 Standard Test Method for Interfacial Tension of Electrical Insulating Oils of Petroleum Origin Against Water by the Drop Weight Method 1 This standard is issued und[.]

Standard Test Method for

Interfacial Tension of Electrical Insulating Oils of Petroleum

This standard is issued under the fixed designation D 2285; the number immediately following the designation indicates the year of

original adoption or, in the case of revision, the year of last revision A number in parentheses indicates the year of last reapproval A

superscript epsilon ( e) indicates an editorial change since the last revision or reapproval.

1 Scope

1.1 This test method covers a comparatively rapid

proce-dure particularly applicable for field use for measuring, under

nonequilibrium conditions, the interfacial tensions of electrical

insulating oils of petroleum origin against water This test

method has been shown by experience to give a reliable

indication of the presence of hydrophilic compounds This test

method may not be applicable for highly viscous insulating

fluids

1.2 This standard does not purport to address the safety

concerns, if any, associated with its use It is the responsibility

of the user of this standard to establish appropriate safety and

health practices and determine the applicability of regulatory

limitations prior to use.

2 Referenced Documents

2.1 ASTM Standards:

D 971 Test Method for Interfacial Tension of Oil Against

Water by the Ring Method2

D 1298 Practice for Density (Specific Gravity) or API

Gravity of Crude Petroleum and Liquid Petroleum

Prod-ucts by Hydrometer Method3

3 Summary of Test Method

3.1 Interfacial tension is determined by measuring the

volume of a drop of water formed in oil A larger water drop

means a higher interfacial tension The instrument is calibrated

to read approximately in millinewtons per metre (dynes per

centimetre) The measurement is completed within 1 min after

the formation of the water drop in oil

4 Significance and Use

4.1 This test method indicates the presence of hydrophilic

compounds These compounds can be an indicator of

contami-nants in new oil and in used oil, oxidation or deterioration of

the oil or materials of construction in contact with the oil

5 Apparatus

5.1 Tensiometer4that provides a simple way of injecting a measured quantity of water into oil The scale attached to the piston forcing the water into the oil is graduated in millinew-tons per metre (dynes per centimetre)

5.2 Test Specimen Container—Glass beaker or transparent

cylindrical vessel having a minimum diameter of 1 in (25.4 mm)

5.3 Needle, supplied with the tensiometer having a blunt

end with a 90° angle Follow manufacturer’s guidelines for selection

6 Preparation of Apparatus

6.1 Wipe the needle free of oil with clean lint free paper, avoiding any upward motion that may embed a bit of fiber on the sharp needle Do not use an oil solvent on the needle or barrel

6.2 Force distilled water through the barrel and needle to clean the inside Only when contamination is suspected should detergents or solvents be used for cleaning, followed by a thorough rinsing with distilled water Detergents will lower interfacial tension results

6.3 Clean the test specimen container by removing any residual oil with petroleum naphtha (see Note 1) or other suitable hydrocarbon solvents followed by washing with a detergent solution Rinse thoroughly with tap water, then distilled water

NOTE 1—Warning: Petroleum naphtha is flammable and harmful if

inhaled.

7 Calibration of Apparatus

7.1 Interfacial tension, in millinewtons per metre (dynes per centimetre), is determined by the following equation:

1

This test method is under the jurisdiction of ASTM Committee D-27 on

Electrical Insulating Liquids and Gases and is the direct responsibility of

Subcom-mittee D27.07 on Physical Test.

Current edition approved March 10, 1999 Published May 1999 Originally

published as D 2285 – 64 T Last previous edition D 2285 – 98.

2Annual Book of ASTM Standards, Vol 10.03.

3

Annual Book of ASTM Standards, Vol 05.01.

4 Use a tensiometer that employs the drop weight principle for measuring interfacial tension The sole source of supply of the apparatus known to the committee at this time is a tensiometer available from Gerin Corp., 1109 7th Avenue, Neptune, NJ 00753 If you are aware of alternative suppliers, please provide this information to ASTM headquarters Your comments will receive careful consideration at a meeting of the responsible technical committee, which you may attend.

AMERICAN SOCIETY FOR TESTING AND MATERIALS

100 Barr Harbor Dr., West Conshohocken, PA 19428 Reprinted from the Annual Book of ASTM Standards Copyright ASTM

Interfacial tension, m N/m 5 R1~D 2 d!~S/R2 !

where:

R1 5 reading of dial (divisions per drop) of water in oil,

R2 5 reading of dial (divisions per drop) of water in air,

D 5 density of water at measuring temperature (0.998 at

20°C and 0.997 at 25°C),

d 5 density of oil at measuring temperature (If density is

not known, use 0.885 average density), and

S 5 surface tension of water in air (72.75 at 20°C and

71.97 at 25°C)

7.2 Thus, the only calibration is in the R2 value, and this

requires a measurement of the volume, in terms of divisions on

the scale, of a drop of water expelled into air, which is saturated

with water vapor to minimize evaporation By properly

approximately nine divisions on the scale

7.3 Calibrate the tensiometer daily to ensure accurate

re-sults

7.4 Perform the calibration check as follows:

7.4.1 Fill the tensiometer barrel with distilled water,

7.4.2 Expel air from the barrel and then clamp the barrel

into position on the mounting stand

7.4.3 Place a glass beaker containing at least 12.7 mm (1⁄2

in.) of distilled water on the mounting stand, bringing the water

ensures the air surrounding the needle is saturated with water

vapor

7.4.4 Note reading on the scale, then expel a single drop of water and note difference of scale reading

7.4.5 The average of ten such “drops in air” is taken as the

orifice calibration of water in air, that is, the R2value 7.5 Any reading deviating as much as 0.2 scale divisions from the average is discarded If any reading is 0.4 or more scale divisions from the average, check instrument for con-tamination and repeat calibration Air leaks in the barrel and dust in the needle are the usual source for variations Variations can also cause unrepeatable results

7.6 Prepare a correction curve showing the total multiplier

versus density, d, using oils with a suitable range of known

densities For an oil having a density different from the

“average density” oil, apply the correction factor to the observed scale reading

8 Procedure

8.1 Apparatus, test specimen, and water should be at a

8.2 Fill the barrel with distilled water

8.3 Expel air from the barrel and clamp the tensiometer into its mount

8.4 Pour oil into the test specimen container to a depth of at least 25.4 mm (1 in.) Do not filter Place the container on the table so that the needle tip is immersed about 12.7 mm (1⁄2in.)

N OTE 2—This test method is a comparatively rapid procedure particu-larly applicable for field use Therefore, filtration adds an undesirable extra step Also, it is anticipated that oil samples drawn from electrical equipment in the field will not contain heavy oil sludge, such as may be found in samples taken at the end of laboratory oxidation tests, which would interfere with the determination of interfacial tension.

8.5 Note the reading on the scale; then expel a trial drop Note the difference in scale readings

8.6 Expel about3⁄4of the volume of water found in 8.5 and allow this drop to remain suspended on needle (age) for about

30 s

8.7 Slowly release enough water to cause the drop to fall so that total time to expel the drop is between 45 and 60 s 8.8 Note the volume of water in the drop in terms of divisions on the scale This reading will give the interfacial tension of an oil of average density

8.9 If more accurate readings are desired, apply the correc-tion factor for the density of the oil under test, using the curve made during the calibration

9 Precision and Bias

9.1 The precision and bias have not been determined This

is a rapid procedure for use under field conditions It gives a semiquantitative answer that is subject to significant error For instances where a test value of known precision is required, use Test Method D 971

10 Keywords

10.1 drop-weight method; electrical insulating oil; IFT; interfacial tension; oil

FIG 1 Vertical Interfacial Tensiometer

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This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years and

if not revised, either reapproved or withdrawn Your comments are invited either for revision of this standard or for additional standards and should be addressed to ASTM Headquarters Your comments will receive careful consideration at a meeting of the responsible technical committee, which you may attend If you feel that your comments have not received a fair hearing you should make your views known to the ASTM Committee on Standards, 100 Barr Harbor Drive, West Conshohocken, PA 19428.